Process for treatment of hydrocarbons



July 4, 1944.` G f A. IBACH PROCESS FOR TREATMENT OF HYDROCARBONS Filed May 26. 1941 INVENTOR G. A. IBACH Patented July 4, 1944 UNITED STATES PATENT OFFICE PROCESS FOR TREATMENT OF HYDROCARBONS Gerald A. Ibach, Phillips, Tex., assignor to Phil-- lips Petroleum Company,

Delaware a corporation of The present invention relates to a process for the thermal conversion of hydrocarbons whereby greatly increased yields of the desired products are obtained and at the same time operating cycles are materially lengthened by elimination of coke and carbonaceous material from the systern.

In petroleum conversion processes, such as the cracking of heavy oils to gasoline and the reforming of lighter oils, it is conventional practice to use tubular heating coils mounted in a suitable furnace in which the petroleum stocks are heated to conversion temperatures under pressure for a sufficient period of time to effect the desired degree of conversion. The converted fluid is then passed through a pipe to a separating .chamber where the fluid is separated into liquid and vapor fractions. This pipe is conventionally referred to as the transfer line. At some point in the transfer line, usually in the immediate vicinity of the separating chamber, is located a pressure relief valve for the purpose of controlling the pressure maintained in the fluid passing through the heating coil.

One of the principal difficulties encountered in the operation of a process such as described above inherent in the cracking-polymerization of hydrocarbon oilsis the formation of coke or carbonaceous products on the walls of tubes and transfer lines which seriously inhibits heat transfer, causes increased pressure drop and shortens still operating cycle. In some respects this invention is an improvement over Patent No. 2,162,- 300, of June 13, 1939, to J. L. Farrell and G. A. Ibach, which describes and claims a process for the treatment of hydrocarbons wherein rmeans are provided in the transfer line between the tubular heating coil and vseparating chamber .for cooling the tar film to prevent the formation and deposit of carbonaceous matter in the transfer line.

Many theories have been advanced as to the cause of coke formation, the most plausible-being that vapors containing tar and polymers in finely divided form moving through a pipe with the turbulent motion attained in most cracking coils,

tively slower speed than the rest of the iluid passing through the line. Consequently the lm is subjected to the hot tube walls and high temperature uid streams for a relatively long period4 of position or coking temperature of the tar lm. As a result, cracking-polymerization reactions take place as the lm is carried along, removing the lighter, lower boiling portion of the tar or polymer and leaving heavy tar, which eventually decomposes to form carbon or coke. This solid material axes itself to the interior of the pipe and builds up to such an extent as to constrict flow and seriously hinder operation of the system.

The present invention has for its object the prevention of carbon formation and deposition in the tube coils and transfer line of a hydrocarbon conversion still.

` A principal object of the invention is to cool and remove from the reaction zone liquid tar and polymers formed under reaction heat at intermediate points in the tube coils.

A further object of this invention is to accomplish removal of carbon forming materials in the tube coils and transfer line of a hydrocarbon conversion still without substantial temperature drop in the main mass of fluid.

More specifically the present invention contemplates the removal from the conversation coil by complementary cooling and centrifugal means, without substantially cooling the main mass of fluid.

The process described in Patent No. 2,162,300 is principally concerned with preventing coke formation in the transfer tubebetween the tubular heating coils and the separating zone.

This is accomplished as described in said patent specification by indirect heat transfer, so controlled that the temperature of the tar film is reduced below the point of coke formation Without substantially reducing the temperature of the remaining prodtotal products in the line.

ucts passing through the passageway. As pointed out in the patent, heat exchangers which involve rapid cooling of the fluid below an active reaction temperature are undesirable, and further i would cause undue 'condensation of low boiling constituents in admixture with the tar film. The rate of heat transfer must be regulated so as to cool the tar film below the coking point without substantially changing the temperature of the This process has proven extremely efficient in maintaining the transfer line and pressure relief valve free of carbonaceous material.

Experience has shown, however, that coke formation occurs to a great extent within the tubular heating coil itself and prior to the point at which the fluid stream enters the transfer line as well as in the transfer line. The deposition time, which temperatureis far above the decom- 65; Qf carbonaceous material in the heating C011 iS particularly undesirable since in addition to shortening operating cycle and causing pressure drop, heat transfer rate is reduced, thereby requiring more fuel to raise the stock to conversion temperature. The formation of coke or carbonaceous material does not occur to an appreciable extent when the charge stock is initially heated in the cracking coil, but as the stream is moved along the passageway under pressure it is raised to a conversion temperature, at which point polymerization and tar formation take place. The resultant nlm, if allowed to proceed through the passageways, will itself undergo decomposition due to the highly heated tube walls, as previously described, to form carbonaceous material which in time builds up to a substantial thickness and clogs the pipe.

I have discovered by observation of the effect of maximum coke formation in return bends in a header box of a cracking furnace, wherein temperatures are in the range of l-800 F. as distinguished from temperatures of from 1000 to 1600 F. in th-e heater proper, and where oil temperatures within the tubes are not materially affected by the slight degree of cooling done in passage through the return bends, that with controlled cooling and continuous separation, preferably by centrifugal means, at intermediate points in the coil, tar and like carbon-forming oils can be removed without substantial lowering of stream temperature. The cooling means which I employ is similar in operation and effect to that described in the aforementioned patent, except that turbulent conditions existing within the cracking coil appear to throw out by centrifugal force the finely divided tar and polymers suspended in the gaseous stream against the relatively cool inner wall of the passageway, where they liquefy andcombine with the previously formed transient tar film. Preferably I employ additional separating means immediately following the cooling zones in the form of cyclone separating chambers which accomplish by centrifugal action further deposition of finely divided material from the fluid stream. Separation is effected by these means as previously described under conditions so controlled that the remaining products pass continuously through the tubular heating coil and transfer line at substantially conversion temperature.

The fluid products in the separating chambers comprising tar, polymers and some heavy oils, depending upon the degree of cooling, are withdrawn and fractionated in a tar stripper tower into tar and various lighter fractions of recycle material. The recycle material may be' taken orf from the tower as side streams and returned to the coil at the proper places for further conversion.

The -cooling zones with supplementally separating chambers are disposed at intermediate points in series with the heating coil outside of the furnace but close enough thereto to avoid substantial temperature drop so as to provide periodic means for withdrawing coke forming material from the conversion products. Generally, the number of units employed in connection with the heating coil will depend on the length of the coil and furnace temperature. High temperatures encourage tar and polymer formationl and therefore require more frequent separation. The units are advantageously located in those regions in the heating coil and transfer line at which coke formation and deposition would take place in the thin film ofconversion products if potential coke forming material were not removed.

The cooling is preferably accomplished by indirect heat exchange With the use of individual cylindrical jackets concentrically arranged about the tube. I prefer to employ the charge stock as the cooling medium which is circulated through the various jackets, although obviously an outside source of fluid may be utilized for this purpose. The cooling jackets are provided with by-passes so that the rate of heat exchange may be accurately controlled to allow the conversion products to pass through the cooling Zones and separating means without substantial change in temperature. Ordinarily, by my method of operation, the temperature of the main mass of converted products will not be lowered more than about 10 F. in passing through the cooling and separating means, and frequently less than 10 F., though this lowering can be increased to some extent without causing undue condensation of high boiling constituents.

The separating chamber, as previously stated, is of the Cyclonic type and materially aids condensation of the suspended tar and polymer material by centrifugal action. Of course a fairly complete separation of liquid constituents may be effected by the cooling means alone, but I prefer the complemental use of centrifugal force which exerts a separating action of its own, for y best results.

In Fig. 1 of the appended drawing I have illustrated diagrammatically one form of apparatus which may be used in practicing my invention. Fig. 2 is a cross-section of one of the separators shown in Fig. 1.

Charge stock, Which may be crude oil or any of its components, including butane-propane, is pumped by the charge pump I through pipe 2 and cooling jacket 3 in indirect heat exchange with transfer line 40 and then through the pipe 6. Part of the charge stock may be diverted through the valve 4 and by-pass 5 to control the temperature in the cooling jacket 3. The fluid is then carried through cooling jacket I which is in indirect heat exchange with the conversion products passing from the tubular heating coil through outlet pipe 36. The degree of cooling is controlled by regulation of valve 8 and by-pass 9 and the fluid stream thereafter conveyed through pipe I0 into jacket II arranged aboutl the Vpipe 2| which leads off from the tubulary jacket I I is conveyed through conduit I4 toccoling jacket I5 which is disposed at an intermediate point in the tubular heating coiland -in this case near the discharge end thereof. The temperature of the charge stock -when it reaches cooling jacket I5 has been considerably raised' due to passage through cool-ing jackets 3, l, and II and in direct heat 'exchange `v'viththe hot conversion products, and therefore the valve IB in the -by-pass II is practically closed' so' that nearly the entire flow of charge 'stock passes through the cooling jacket. The partially heated fluid stream passes from cooling 'jacketsl I5` through pipe I8 and into the first section .I9 off theY tubular heating coil which is located withinl furnace '20. The charge stock is raised'to a con-J version temperature within the` heating coil and passes from the section I9 through vpipe 2l and cooler ll in indirect heat exchangewith the charge stock and thereafter tangentially into the cyclone separating chamber 22 which throws out-by centrifugal action finely divided material suspended in the gaseous stream. `The conversion products, free of tar and polymers, pass upwardly through the conduit 28 and back into Vthe furnace proper while liquid products collecting in the bottom of the chamber 22 are withdrawn through valve 23 and pipe 24, conduits 25 and 26, to the tar stripper and fractionating tower 21. These liquid productsA consist of tar, polymers and other high boiling liquid conversion products. Conversion products pass from the conduit 28 at conversion temperature into the section 2.9 of the heating coil and then through the cooling jacket I5 by means of the pipe 33 .and into the separating chamber 3|, thereafter being returned to the furnace overh'ead through the pipe 34. The liquid products are withdrawn from the bottom of separating chamber 3| through valve 32 and pipe 33 where they are combined with tar and polymers withdrawn from chamber 22 yin the conduit 25. Remaining conversion products pass through section of the heating coil, are further heated, and flow from the furnace to the transfer line located between the heating coil and separating means. I have found it advantageous to employ one or more cooling jackets and separating chambers in the transfer line and therefore the hot conversion products, as they emerge from the furnace through the discharge pipe 36, are passed through cooling jacket 1 and into the separating chamber 31. The conversion products pass upwardly through pipe 40 and additional cooling jacket 3, while deposited cokeforming materials are withdrawn from the separating chamber through valve 38 and pipe 39 to conduit 25. The conversion products, after passing through cooling jacket 3 and separating chamber 4l, are then conveyed through pipe 44 and pressure control valve to the separating tower and expansion chamber 46, while liquid products withdrawn from the bottom of the separating chamber 4I through valve 42 and pipe 43 combine with liquid products withdrawn from the other separating chambers in conduit 25. In separating tower 46 the gaseous conversion products, including condensibles and non-condensibles, are freed from heavy tar and polymer material, and pass overhead through valve 41 and pipe 48 for fractionation or recycle by means not shown. The recycle fraction may be returned to the charge pump or coil at proper points where similar material is undergoing treatment in a manner now described for the treatment of residuum.

Tar, polymer material and possibly small quantities of heavy oil which were condensed along with tar particles are withdrawn from the bottom of gas separator tower 46 and passed into the fractionating tower 21 through pipe 26, together with fluid products passing through separator collector header 25. The heavy materials entering this tower are conveyed to a flash or stripping section employing trays, where separation is effected between heavy tar and recycle material. The recycle material may be drawn off as sidestreams and returned to the cracking coil at the proper points where hydrocarbons of similar molecular weight are being converted.

This is shown diagrammatically by the dotted linesgfromthe tar-.stripper tower to the conversion coil,'and maybe accomplished without material temperature drop in a continuous cycle. Lower .boiling material may be withdrawn through'pipe 49 and valve 50.

By the present invention, I provide a process for the continuous conversion of hydrocarbon material with means for withdrawal of tar and cokeforming constituents at intermediate points of the system, and further means whereby these materials may be fractionated into recycle stock and continuously returned to the conversion coil at the proper points at which similar material is undergoing treatment. This is accomplished without affecting the operation of the cracking coil, since separation takes place without substantial change in temperature. Thus not only is coking and clogging of the tubular heating coil and transfergline prevented, but an economical recovery and recycle of tar, polymer and heavy oil constituents is effected which are thus converted into valuable products.

I claim:

1. An improved process for the thermal vapor phase conversion of high boiling hydrocarbons into lower boiling products, which comprises subjecting a continuously flowing stream of such hydrocarbons under an elevated pressure and in `vapor phase to an elevated conversion temperature inan elongated conversion zone of restricted cross-,sectional area for a time such as to effect only a partial conversion to lower boiling products together with the formation of only a minor amount of heavy hydrocarbons and tar which collect on the bounding surface of said conversion zone, subjecting the surface of a short section of said zone to indirect cooling. to reduce below coking temperature heavy hydrocarbons and tars collected thereon and limiting the extent of said cooling such that the temperature of the hydrocarbons undergoing conversion is not reduced more than 10 F., removing said cooled heavy hydrocarbons and tar from said surface while maintaining said conversion temperature and pressure, repeating the steps of partial conversion and limited cooling of the bounding surface and removal of heavy hydrocarbons and tars atleast one additional time, reducing the pressure on the final conversion eiiluent and passing same to a rst separation zone, removing low boiling products of said conversion from said eluent in said separation zone, removing also from said eiiiuent higher boiling hydrocarbons, admixing with said higher boiling hydrocarbons heavy hydrocarbons and tar removed from intermediate points in said conversion, passing said combined materials to a second separating zone, removing from said second separating zone at least one high boiling hydrocarbon fraction and returning said fraction to an intermediate point in said conversion.

2. An improved process for the thermal vapor phase conversion of high boiling hydrocarbons into lower boiling products, which comprises subjecting a continuously flowing stream of such hydrocarbons under an elevated pressure and in vapor phase to an elevated conversion tempera- Iture in an elongated conversion zone of restricted cross-sectional area for a time such as to effect only a partial conversion to lower boiling products together with the formation of only a minor amount of heavy hydrocarbons and tar which collect on the bounding surface of said conversion zone, subjecting the surface of a short section of said zone to indirect cooling to reduce below coking temperature heavy hydrocarbons and tars rtaining said conversion temperature-and pressure,

repeating the steps of partial conversion and limited cooling of the bounding surface and removal of heavy hydrocarbons and tars atleast one additional time, reducing the pressure 'on the final conversion eliluent and passing samel to a iirst separation zone, removing 10W boiling products of said conversion from said eiiluen't in said separation zone, removing also from said eiTluent higher boiling hydrocarbons, admixing with said higher boiling hydrocarbons heavy hydrocarbons and tar removed from intermediate points in said conversion, passing said combined materials to a second separating Zone, removing from said second separating zone a lighter high boiling hydrocarbon fraction and a heavier high boiling hydrocarbon fraction, returning said lighter fraction to the rst part of said conversion zone, and returning said heavierfraction to the latter part of said conversion zone.

3. An improved process for thel thermal conversion of hydrocarbons in the vapor phase, which comprises subjecting a continuously owing stream of a hydrocarbon material in-vapor phase to an elevated conversion temperature in an elongated conversion zone of restricted cross-sectional area for a time such as to effect only a partial conversion and formation of only a minor amount of` heavy hydrocarbons and tar which collect on the bounding surface of said conversion zone, subjecting the surface of a short section of said conversion zone to indirect cooling to reduce below coking temperature heavy hydrocarbons and tar collected thereon and limiting the extent of said cooling such that the temperature of the main body of hydrocarbon material is not reduced more than 10 F., removing said cooled heavy hydrocarbons and tar from saidsurface While maintaining :said conversion temperature and pressure, repeating the steps of partial conversion and limited cooling. of the bounding surface and removal of heavy hydrocarbons and tars at least one additional time, reducing the pressure on the nal conversion eiluent and passing same to a first separation zone, removing low boiling products of said conversion fro-m said effluent in said separation zoneremoving also from said etiluent higher boiling hydrocarbons, admixing with said higher boiling hydrocarbons heavy hydrocarbons and tar removed from intermediate points insaid conversion, passing said combined materials to a second separating zone, and removing from said second separating zone asv an overhead product a hydrocarbon fraction comprising higher boiling products of said conversion.

GERALD A, IBACH. 

